1. Field of the Invention
The present invention relates to a process of producing a polarizer and a polarizer obtained by the process concerned. And the present invention relates to a polarizing plate using the polarizer concerned. Furthermore, a visual display, such as a liquid crystal display, an organic EL display, a PDP (plasma display panel), using the polarizing plate concerned.
2. Description of the Prior Art
Heretofore, as a polarizer used in a liquid crystal display or the like, a polyvinyl alcohol film dyed with iodine has been used since the polarizer has both of a high transmittance and a high polarization degree. The polarizer is usually used as a polarizing plate laminating, on its single side or both sides, a protective film such as the films made of triacetylcellulose.
In recent years, a liquid crystal display becomes to be broadly used, and, in connection with expansion of use it is often used under high temperature conditions etc. for a long period of time. And a liquid crystal display having little change of hue according to usage becomes to be required. In connection with those demands, durability avoiding giving degradation of optical property is also required to a polarizing plate, when it is left under high temperature conditions, or under high temperature and high humidity conditions.
For example, in Japanese Patent Laid-Open Publication No. S54-16575, Japanese Patent Laid-Open Publication No. S61-175602, and Japanese Patent Laid-Open Publication No. 2000-35512, it is described that durability of a polarizer comprising poly vinylalcohol based film that is dyed by iodine may be improved by making it contain suitable quantity of zinc ion. In detail, as an example of durability, it is shown there that red discoloration (polarization defect of long wavelength light) in crossed-Nicols generated in the case where it is left especially under high temperature condition can be prevented. In methods manufacturing a polarizer described in these official gazettes, processing in which zinc ion is included in the polarizer is performed by treating the polarizer with a solution including boric acid, zinc ion, and iodine ion simultaneously. However, when zinc ion is impregnated by such methods, some amount of processing liquid may remain on a surface of the polarizer taken out from impregnating bath. And then boric acid may deposit when the polarizer is dried, leading to a problem of appearance fault in the case where it is adhered with protection films. Moreover, when the processing is given in a final stage of stretching process, as also in case of zinc ion, deposit generated from zinc ion sometimes gives appearance fault to protection films adhered when the polarizer is dried.
An object of the present invention is to provide a process of producing a polarizer comprising poly vinylalcohol based film having good durability that is dyed by iodine, and is given boric acid processing, and moreover contains zinc without generating fault by deposit of boric acid or zinc.
And other object of the present invention is to provide a polarizer obtained by the producing process, a polarizing plate utilizing the polarizer and further a visual display utilizing the polarizing plate.
As a result of repeated examinations carried out wholeheartedly by the present inventors to solve the above-mentioned problems, a process of producing a polarizer shown below was found out and the present invention was completed.
Namely the present invention relates to a process of producing a polarizer, comprising the steps of: conducting dyeing by iodine to unstretched poly vinylalcohol film; subsequently conducting uniaxial stretching processing and boric acid processing; conducting impregnation processing by zinc; and furthermore conducting impregnation processing by iodine ion.
In the process of producing the above-described polarizer, uniaxial stretching processing and boric acid processing are preferably simultaneously carried out.
In the above-described process of producing the polarizer, as described above, when impregnating processing by iodine ion is conducted after boric acid processing and impregnating processing by zinc, deposit generation of boric acid and zinc are inhibited, consequently leading to realization of a polarizer having satisfactory outward appearance and satisfactory durability. Furthermore, when uniaxial stretching processing and boric acid processing are carried out simultaneously, a polarizer having high polarization performance will preferably be obtained.
And the present invention relates to a polarizer obtained by the above described process.
And the present invention relates to a polarizing plate with which a transparent protective layer is prepared at least in one side of the above described polarizer.
In the above-mentioned polarizing plate, comprising at least one of a retardation plate, a viewing angle compensation film, a reflector, a transflective plate and a brightness enhancement film, is used.
Furthermore, the present invention relates to a visual display using the above-described polarizing plate.